1. Field of the Invention
The present invention relates to an apparatus and a method for controlling a transmission for a straddle-type vehicle and, in particular, for controlling a transmission having a dog-clutch mechanism.
2. Description of the Related Art
Some vehicle transmissions have a main shaft connected to an engine's crankshaft via a clutch and a countershaft that outputs the torque of the engine to the wheel. The transmission can also include a first gear having an engaging portion (e.g., dog-teeth in a dog-clutch) and a second gear having engaged portion (e.g., dog-holes in a dog clutch). The main shaft can pass through the first gear, which is rotationally coupled to the main shaft by splines provided on the countershaft. The main shaft also passes through the second gear, which can ride on bearings such that the second gear idles relative to the main shaft. The transmission moves the first gear along the main shaft with a shift fork to bring the second gear into engagement with the first gear, thereby engaging the gears. With respect to a dog-clutch, when the first gear engages the second gear, the dog-teeth in the first gear engage the dog-holes in the second gear.
With such transmissions, when the vehicle is at a standstill, as the dog-tooth gear (i.e., first gear) and the dog-hole gear (i.e., second gear) are brought towards each other, the gears sometimes cannot be engaged because the engagement portions collide. The engagement portions can collide because the rotation of the main shaft stops when the vehicle is standing still causing the dog-teeth to remain offset from the dog-holes. This situation can also occur in electric transmissions when the actuator moves the dog-tooth gear into engagement with the dog-hole gear.
Some conventional electric transmissions have monitored the shifting speed of the dog-tooth gear during gear engagement. For example, when the shifting speed reaches zero the transmission determines that dog collision has occurred. These electric transmissions may rotate the dog-tooth gear or the dog-hole gear by the torque of the motor upon determining that dog collision has occurred, thereby resolving the dog collision.